How Groundwater Sustainability Affects San Lorenzo River Flow

Did you know that 40 to 50% of dry season flow of the San Lorenzo River comes from the Santa Margarita Basin?

Groundwater, like that from the Santa Margarita Basin, and surface water are closely connected. Throughout the San Lorenzo River and its tributaries, there are places where groundwater surfaces and supplies baseflow to the river (gaining) as well as places where the surface water infiltrates and goes underground (losing). Depleted groundwater levels can cause a historically gaining stream to cease to receive groundwater, and possibly even become a losing stream. This can reduce the flow in the river, particularly in the dry months, which can in turn be a devastating blow to local salmonid species. That’s why it’s critical that we monitor and manage groundwater basins.

Groundwater levels in the Santa Margarita Basin have dropped approximately 200 feet from historical levels. Thanks to increased conservation efforts implemented by the water districts, groundwater levels stabilized in the mid-1990s. While they have remained fairly steady over the past 20 years, there has been no noticeable trend towards groundwater level recovery. Therefore, the basin is currently facing surface water depletion, reduction of storage, degraded water quality and lowering of groundwater levels.

Up until recently, water agencies worked fairly independently in managing water resources (though this region does have a history of collaboration). That changed in 2015 with the Sustainable Groundwater Management Act. The act requires that certain groundwater basins form a Groundwater Sustainability Agency to prepare a Groundwater Sustainability Plan bring that basin into sustainability by 2042. The Santa Margarita Groundwater Agency was formed as a result, uniting the County of Santa Cruz, Scotts Valley Water District, the San Lorenzo Valley Water District and other stakeholders in a Joint Powers Authority. The Santa Margarita Groundwater Agency is one of three groundwater management agencies formed in Santa Cruz County.

The process to develop the Groundwater Sustainability Plan to address the depleted groundwater level is just beginning. To stay informed and participate in the process, here is what you can do: